From hungtao at stanford.edu  Tue Jun 14 10:06:54 2005
From: hungtao at stanford.edu (Hung-Tao Chou)
Date: Tue, 14 Jun 2005 10:06:54 -0700
Subject: photoresist residue problem
Message-ID: <1118768814.42af0eae9c24f@webmail.stanford.edu>

Hi all,

I used PQuest to etch GaN and used photoresist (Shipley 1813) as a mask.
After etching and immersing the sample in acetone, I still found a lot of
photoresist residue on my sample (the attached jpg).  Does anyone have
similar experience and have suggestions on how to remove the residue? I
have put my sample into warm acetone overnight (60C) but it only removed
the residue very slowly.

Thanks in advance

Hungtao
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From jimkruger at yahoo.com  Tue Jun 14 10:49:38 2005
From: jimkruger at yahoo.com (jim kruger)
Date: Tue, 14 Jun 2005 10:49:38 -0700 (PDT)
Subject: photoresist residue problem
In-Reply-To: <1118768814.42af0eae9c24f@webmail.stanford.edu>
Message-ID: <20050614174938.72131.qmail@web40910.mail.yahoo.com>

I am guessing that to etch GaN, you heated the system
and used a chip mounted on a carrier wafer.  Standard
photoresists are novolac based so will crosslink at
temperatures above about 150 C  (I saw little
crosslinking at 180 C in air but strong crosslinking
at 230 C in air).  The crosslinked novolac is
basically Bakelite -  (plastic ashtray material) and
not soluble.  Radiation can induce crosslinking at
lower temperatures.

 I believe it will be removed by oxygen plasma if your
chip can stand that.

 If the heating caused to much pattern distortion, it
is possible to UV/heat stabilize the resist in
advance.  Then only oxygen plasma will remove the
resist (I presume sulfuric-peroxide is out of the
question).

I hope this helps. I would be glad to discuss it in
further detail.

PS I am an Industrial User with long process
experience in industry and am always glad to talk to
students, especially plasma questions.

jimkruger

--- Hung-Tao Chou <hungtao at stanford.edu> wrote:

> Hi all,
> 
> I used PQuest to etch GaN and used photoresist
> (Shipley 1813) as a mask.
> After etching and immersing the sample in acetone, I
> still found a lot of
> photoresist residue on my sample (the attached jpg).
>  Does anyone have
> similar experience and have suggestions on how to
> remove the residue? I
> have put my sample into warm acetone overnight (60C)
> but it only removed
> the residue very slowly.
> 
> Thanks in advance
> 
> Hungtao
> 



		
__________________________________ 
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Stay in touch with email, IM, photo sharing and more. Check it out! 
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From hungtao at stanford.edu  Tue Jun 14 11:09:30 2005
From: hungtao at stanford.edu (Hung-Tao Chou)
Date: Tue, 14 Jun 2005 11:09:30 -0700
Subject: photoresist residue problem
In-Reply-To: <20050614174938.72131.qmail@web40910.mail.yahoo.com>
References: <20050614174938.72131.qmail@web40910.mail.yahoo.com>
Message-ID: <1118772570.42af1d5a7a385@webmail.stanford.edu>

Dear Jim,

Thank you so much for your information. In my etch recipe, I do heat up the
system up to 80 C and mount a sample on a carrie wafer.

For using oxygen plasma to clean the photoresist, do you have any
suggestions on how long the clean time should be? My photoresist is about
1um thick.  Also on my GaN chip I have Al (200nm)/Ti (10nm) as ohmic
contacts, do you think will the O2 plasma affect the Al/Ti ohmic contacts?
Or it will only oxidize the surface of Al layer?

Thanks again!

Hungtao

Quoting jim kruger <jimkruger at yahoo.com>:

> I am guessing that to etch GaN, you heated the system
> and used a chip mounted on a carrier wafer.  Standard
> photoresists are novolac based so will crosslink at
> temperatures above about 150 C  (I saw little
> crosslinking at 180 C in air but strong crosslinking
> at 230 C in air).  The crosslinked novolac is
> basically Bakelite -  (plastic ashtray material) and
> not soluble.  Radiation can induce crosslinking at
> lower temperatures.
>
>  I believe it will be removed by oxygen plasma if your
> chip can stand that.
>
>  If the heating caused to much pattern distortion, it
> is possible to UV/heat stabilize the resist in
> advance.  Then only oxygen plasma will remove the
> resist (I presume sulfuric-peroxide is out of the
> question).
>
> I hope this helps. I would be glad to discuss it in
> further detail.
>
> PS I am an Industrial User with long process
> experience in industry and am always glad to talk to
> students, especially plasma questions.
>
> jimkruger
>
> --- Hung-Tao Chou <hungtao at stanford.edu> wrote:
>
> > Hi all,
> >
> > I used PQuest to etch GaN and used photoresist
> > (Shipley 1813) as a mask.
> > After etching and immersing the sample in acetone, I
> > still found a lot of
> > photoresist residue on my sample (the attached jpg).
> >  Does anyone have
> > similar experience and have suggestions on how to
> > remove the residue? I
> > have put my sample into warm acetone overnight (60C)
> > but it only removed
> > the residue very slowly.
> >
> > Thanks in advance
> >
> > Hungtao
> >
>
>
>
>
> __________________________________
> Discover Yahoo!
> Stay in touch with email, IM, photo sharing and more. Check it out!
> http://discover.yahoo.com/stayintouch.html
>




From scaccag at stanford.edu  Sun Jun 19 20:43:37 2005
From: scaccag at stanford.edu (Luigi Scaccabarozzi)
Date: Sun, 19 Jun 2005 20:43:37 -0700 (PDT)
Subject: photoresist residue problem
In-Reply-To: <1118772570.42af1d5a7a385@webmail.stanford.edu>
Message-ID: <Pine.GSO.4.44.0506192040460.27955-100000@elaine43.Stanford.EDU>

Hungtao,
I had similar problems. A good way to remove the resist is in HOT 1165
(~60C) in sonic bath, for at least 30 min 9you can do that in the solvent
bench). If you cannot use sonics becasue you have fragile structures, the
only way that I know is O2 plasma (DryTek4), although in my case the
sample was not completely cleaned up even after a long O2 plasma.
Gigi

On Tue, 14 Jun 2005, Hung-Tao Chou wrote:

> Dear Jim,
>
> Thank you so much for your information. In my etch recipe, I do heat up the
> system up to 80 C and mount a sample on a carrie wafer.
>
> For using oxygen plasma to clean the photoresist, do you have any
> suggestions on how long the clean time should be? My photoresist is about
> 1um thick.  Also on my GaN chip I have Al (200nm)/Ti (10nm) as ohmic
> contacts, do you think will the O2 plasma affect the Al/Ti ohmic contacts?
> Or it will only oxidize the surface of Al layer?
>
> Thanks again!
>
> Hungtao
>
> Quoting jim kruger <jimkruger at yahoo.com>:
>
> > I am guessing that to etch GaN, you heated the system
> > and used a chip mounted on a carrier wafer.  Standard
> > photoresists are novolac based so will crosslink at
> > temperatures above about 150 C  (I saw little
> > crosslinking at 180 C in air but strong crosslinking
> > at 230 C in air).  The crosslinked novolac is
> > basically Bakelite -  (plastic ashtray material) and
> > not soluble.  Radiation can induce crosslinking at
> > lower temperatures.
> >
> >  I believe it will be removed by oxygen plasma if your
> > chip can stand that.
> >
> >  If the heating caused to much pattern distortion, it
> > is possible to UV/heat stabilize the resist in
> > advance.  Then only oxygen plasma will remove the
> > resist (I presume sulfuric-peroxide is out of the
> > question).
> >
> > I hope this helps. I would be glad to discuss it in
> > further detail.
> >
> > PS I am an Industrial User with long process
> > experience in industry and am always glad to talk to
> > students, especially plasma questions.
> >
> > jimkruger
> >
> > --- Hung-Tao Chou <hungtao at stanford.edu> wrote:
> >
> > > Hi all,
> > >
> > > I used PQuest to etch GaN and used photoresist
> > > (Shipley 1813) as a mask.
> > > After etching and immersing the sample in acetone, I
> > > still found a lot of
> > > photoresist residue on my sample (the attached jpg).
> > >  Does anyone have
> > > similar experience and have suggestions on how to
> > > remove the residue? I
> > > have put my sample into warm acetone overnight (60C)
> > > but it only removed
> > > the residue very slowly.
> > >
> > > Thanks in advance
> > >
> > > Hungtao
> > >
> >
> >
> >
> >
> > __________________________________
> > Discover Yahoo!
> > Stay in touch with email, IM, photo sharing and more. Check it out!
> > http://discover.yahoo.com/stayintouch.html
> >
>
>



From mcvittie at snf.stanford.edu  Mon Jun 20 09:54:31 2005
From: mcvittie at snf.stanford.edu (Jim McVittie)
Date: Mon, 20 Jun 2005 09:54:31 -0700
Subject: photoresist residue problem
References: <1118768814.42af0eae9c24f@webmail.stanford.edu>
Message-ID: <42B6F4C7.8A56031C@snf.stanford.edu>

Hung-Tao,

First, can you give me details for your etch PQ process. I personally do not
like to use acetone for stripping PR because I have had problems in the past
in removing PR with acetone from Si after non-plasma processes. If you can use
a hot (80C) commercial wet stripper, such as 1165, PRS1000 or PRX127, they
tend to be much better strippers than acetone. Note that in VLSI Si
processing, acetone is never used.  PRX127 is designed to be used as a post
plasma etch stripper when etching Al. I do not know how well GaN will hold up
to it. As Gigi pointed up in his note, O2 plasma is an alternative to wet
stripping. O2 stripping is a temperature activated process. Commercial plasma
strippers usually heat the wafer to speed up the strip rate. Both the GasSonic
and Matix strippers heat the wafer to around 200C and remove a micron of
resist in < 1 min. Without heat the Gasonic rate around 100A / min. You cannot
put GaN into the Gasonic. In principle, you could use the Matix but it is set
up for full 4" wafers so pieces are a problem.  A number of  III-V users have
used Drytek4 for stripping. It has a slow removal rate since it is not heated.
It operated in the RIE mode, which means your samples will be bombarded with
up to 100 eV ions. Strippers, such as the Gasonics and the Matix, operate in
the downstream mode where there is no ion bombardment of the sample/wafer.
This bombardment can cause damage to sensitive surfaces.  Ion bombardment is
not all bad. It speeds up the strip rate and helps remove heavily cross linked
resist. So far, III-V uses have not reported any damage problem with using
Drytek4 for stripping.


Hung-Tao Chou wrote:

> Hi all,
>
> I used PQuest to etch GaN and used photoresist (Shipley 1813) as a mask.
> After etching and immersing the sample in acetone, I still found a lot of
> photoresist residue on my sample (the attached jpg).  Does anyone have
> similar experience and have suggestions on how to remove the residue? I
> have put my sample into warm acetone overnight (60C) but it only removed
> the residue very slowly.
>
> Thanks in advance
>
> Hungtao
>
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